In screening and basic research utilizing cells, there is a known apparatus in the related art for automatically acquiring microscope images of cells (for example, see Patent Document 1).
Automatic focusing of the cell image in Patent Document 1 is performed by using a so-called contrast autofocus process in which the distance between the microscope objective lens and a sample is changed multiple times by an appropriate distance using a motorized alignment mechanism, and the image quality at each position is compared, for example, to select the image with the highest contrast.
As the contrast method in the apparatus described, above a method in which a high-frequency region of the image area is found by using a high-pass filter and the position of maximum contrast in this high-frequency region is set as the focal position is used.
Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2006-58642.